1. Field of the Invention
This invention relates generally to means for guiding machines which orbit the circumference of pipe while performing their functions, and more particularly to a link chain guide for use with a plurality of pipe sizes and one which assures that the machines will define a generally circular path lying in a plane perpendicular to the longitudinal axis of the pipe.
2. Background Art
The types of machines for which the present invention is applicable are well known and include those that, in performing their functions, must orbit the circumference of pipe in a circle lying in a plane perpendicular to the longitudinal axis of the pipe. Such devices include orbital pipe cutting and beveling devices and ultrasonic inspection devices. An example of the former type of device is the VERSIFLAME.RTM. Pipe Cutting & Beveling Machine manufactured by Mathey International Limited Inc. These types of devices may be driven by either electric, pneumatic, or hydraulic motors or they may be manually advanced.
The essential problem of causing a machine to orbit a pipe in a true circle derives from the fact that most pipe is not true dimensionally. The pipe is sometimes oval, sometimes conical, or sometimes conical in two directions on the same pipe; and, consequently, straight cutting or inspecting of pipe utilizing machinery tracking on and dependent upon the surface O.D. of the pipe is very difficult. With pipe which is not true dimensionally, unless some type of guiding mechanism is provided to urge the machine to travel in a circle in a plane perpendicular to the longitudinal axis of the pipe, the machine will actually tend to follow a helical path relative to the perpendicular axis of the pipe.
Conventionally, such machines are rotated about the pipe on a ring containing a rack-gear-and-pinion arrangement. The advantage of this system when cutting pipe is that the torch follows the true path of the ring. The disadvantages are that, first, if the pipe is not round, but oval, an out-of-round attachment is required in order to maintain a constant torch-tip-to-cut-surface distance. Second, such rings are limited in pipe diameter cutting sizes so that it is necessary to have many rings and gears to cut only conventional pipes from 4" O.D. to 36" O.D. This makes the accessories required for such machines very expensive. Other conventional techniques employed to maintain a true path utilize a metal belt which is wrapped around the pipe and on its edges, the orbital machine travels. This system likewise is expensive, requiring many different belts for a range of pipe sizes. Another system of orbital machines, and the one for which the present invention is primarily intended, travel around the circumference of the pipe on wheels, or bogies, and may be propelled by a variety of means. This latter system also suffers from the problems of true circular tracking discussed above, when pipe is not true dimensionally.
It is a principal object of the present invention to provide means by which it is possible when utilizing an orbital machine tracking on the pipe surface, to track on a path lying in a plane perpendicular to the longitudinal axis of the pipe.
It is another object of the invention to provide such a device which can accomplish the above ends using a minimum of accessory equipment, while being able to be employed for a large range of pipe sizes.
Other objects of the present invention will in part be obvious and will in part appear hereinafter.